Download Biology 20 DNA Replication What do the initials DNA stand for

Biology 20
DNA Replication
What do the initials DNA stand for?
DNA History:
1940's:
1947: Chargaff
Chargaff's Rule
1950's:
Early 1950's: Rosalind Franklin:
X-ray crystallography of DNA
1952: Hershey & Chase: (p. 185; Fig. 10.1)
Discovered DNA is the genetic material of bacteriophages (p. 183; Fig. 10.0)
Bacteriophages are viruses that infect bacteria (bacteria eaters)
Conclusions: viral DNA injected into bacteria, which made more viruses
1953: Watson & Crick:
Used information from Franklin's X-ray photos to make a wire scale model
Conclusions:
Late 1950's: Messelson & Stahl
Working with bacteria (E. coli)
Confirmed Watson & Crick's model for DNA replication
Brief review of DNA structure:
DNA is a polymer of?
Components of a nucleotide: (p. 186; Fig. 10.2A)
a)
b)
c)
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Two classes of nitrogenous bases: (p. 187; Fig. 10.2 B & C)
a) Purines
1)
2)
b) Pyrimidines
1)
2)
3)
Which nitrogenous base is only found in RNA?
Which nitrogenous base is only found in DNA?
Which nitrogenous bases are found in both DNA and RNA?
Base pairing of nitrogenous bases (Chargaff's Rule):
Pyrimidines
Base pairs
# of H-bonds
Purines
Adenine (A)
Thymine (T)
A=T
Guanine (G)
Cytosine (C)
G=C
Adenine comprises 20% of the nitrogenous bases in the DNA of a particular organism.
What percentage does cytosine comprise?
DNA structure:
Double helix - shaped like a ladder (p. 189; Fig. 10.3C)
a) Backbone (legs) of the ladder composed of:
b) Rungs of the ladder composed of:
Double helix: 2 nm, suggested 2 strands
10 nucleotide pairs in each helix turn
DNA strands are antiparallel (p. 191; Fig. 10.5B)
Why would a cell undergo DNA replication?
What phase of the cell cycle does DNA replication take place? (p. 131; Fig. 8.5)
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DNA Replication (synthesis):
Enzymes involved in DNA replication:
•
helicase, single strand binding protein, primase:
•
DNA polymerase:
•
DNA ligase:
a)
b)
c)
Origins of replication: (p. 191; Fig. 10.5A)
Replication bubble:
Eukaryotes: thousands of replication bubbles
Why?
Replication Fork: (p. 191; Fig. 10.5C)
Replication bubble creates a Y-shaped region
Replication will spread in both directions:
Priming for DNA Replication:
Before DNA polymerase can begin work on the daughter strands, a primer must be laid first.
Which enzyme produces the primer?
What type of molecule is the primer?
Synthesis of the new DNA strands:
Once the RNA primers are in place, DNA polymerase can go to work.
DNA polymerase catalyses the synthesis of the new strands:
Direction of synthesis:
Why?
Leading strand:
A different DNA polymerase will come and convert the RNA primer to DNA nucleotides
Lagging strand:
Okazaki's fragments:
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Role of DNA ligase:
Semi-conservative model for DNA Replication:
Watson & Crick suggested & Messelson & Stahl confirmed:
DNA template
New DNA strand
New DNA strand
DNA template
Proofreading:
DNA Repair:
Damage to DNA through:
Excision repair:
DNA Technology:
•
Recombinant DNA technology:
•
Polymerase Chain Reactions (PCR): p. 242; Fig. 12.12
•
Restriction Fragment Length Polymorphism (RFLP):
Restriction enzymes:
Use of RFLP's:
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